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Question 765923: Dear all
I have prepared two solutions with different percentage 4% and 2% then I mixed 5 ml from each of the solutions. finally I got 10 ml solution. What is the final concentration by %.
Thank you
Answer by MaartenRU(13)   (Show Source):
You can put this solution on YOUR website! Let's say it's a solution of sugar. It doesn't matter what it is, but it makes the explanation easier.
You have 5ml of a 4% solution. That means that your 5ml solution is 4% sugar.
4% of 5ml is 4/100 of 5ml, so that's 0.2ml of sugar. (Using a volume for sugar seems a bit weird, but that doesn't matter right now)
In the same way, you have 5ml of a 2% solution. 2% of 5ml is 2/100 of 5ml, so that's 0.1ml of sugar.
Now you're mixing the solutions into one big solution. That means that you're also adding up the sugar. So 0.2ml from the one mixture and 0.1ml from the other, amounts to 0.3ml in the total 10ml solution.
Now we only have to find out what percentage 0.3ml is of 10ml.
That's quite simple! We find the fraction and multiply it by 100. So 0.3/10, that's 0.03. Now multiplying it by 100 gives us 3%.
You might find that this is the average of your 2% and 4%, but watch out! You can only take the average if the solutions have the same volume. See for yourself what happens if you take different volumes. As an exercise, try to work out what solution you will get from mixing 5ml of 2% and 10ml of 5%.
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